Electrical heater and plug

ABSTRACT

An electrical heater, to be powered from an automotive-type cigarette lighter socket, includes a heating element, a plug configured to be inserted into the cigarette lighter socket, and a pair of conductors permanently connecting the heating element to the plug. The plug has a flat substrate and a pair of conductors mounted on the substrate. An electrical plug, for a lighter socket of the kind having an inner wall of a predetermined diameter and a pair of electrical contacts, includes a flat assembly having a flat dielectric base having a width corresponding to the predetermined diameter, and a pair of flat conductors attached to the base for touching the pair of electrical contacts in the socket.

This is a continuation of copending application Ser. No. 07/378,144,filed on July 11, 1989, now abandoned, which is a divisional of Ser. No.07/276,376, filed Nov. 23, 1988, now U.S. Pat. No. 4,933,534.

BACKGROUND OF THE INVENTION

This invention relates to electrical heaters powered from automotivetype cigarette lighter sockets, and to electrical plugs for suchsockets.

Such an electrical heater could be used, for example, to keep a pizzapie warm on the way home from the pizza shop. It has been proposed toput such a heater directly into the cardboard pizza box beneath thepizza or to include it in a carrier into which the cardboard box isplaced. The heater is powered from the cigarette lighter socket via aplug. It is known to use such plugs to power a wide variety ofelectrical devices.

SUMMARY OF THE INVENTION

In one aspect, the invention provides an electrical heater, completewith a plug for an automotive cigarette lighter socket, whoseconfiguration and materials are so economical and simple to fabricatethat the entire device may be discarded after use.

One general feature of the invention is the combination of a heatingelement, a plug configured to be inserted into the cigarette lightersocket, and a pair of conductors permanently connecting the heatingelement to the plug.

In another general feature of the invention, the cable connecting theheating element to the plug has a flat substrate and a pair ofconductors mounted on the substrate.

Preferred embodiments of the invention include the following features.The conductors comprise wires. The flat substrate comprises two layersof biodegradable paper (held together by adhesive) with the conductorssandwiched between the layers. The heating element and the plug comprisesubstrates bearing flat conductive layers. The heating element includesa flexible substrate (e.g., biodegradable paper) bearing a resistancecoating (e.g., deposited metal). The cable has a periodic series oftransverse folds along the length of the substrate. The plug includes aflat substrate having a width corresponding to (e.g., slightly greaterthan) the diameter of the cigarette lighter socket, and a pair ofconductors attached to the substrate for touching a pair of contacts inthe lighter socket. The substrate of the plug is, e.g., a sheet ofplastic laminated paper. The plug has a series of teeth located to touchthe inner wall of the socket, each tooth having a more tapered leadingedge to make insertion of the plug easier, and a less tapered trailingedge to make removal of the plug more difficult. One of the flatconductors of the plug lies along an axis of the plug for makingconnection with a central contact of the socket, and that conductorextends beyond the end of the substrate and has a contour which providesresilience to the conductor in the direction of the axis of the plug.

Another general feature of the invention is the plug itself.

Food (e.g., pizza pie) and other items may be kept warm while intransit. In the case of pizza, the devices are so inexpensive that theycan be given away to the customer with the pizza box. The invention canbe stored compactly and conveniently, ready for use, and can be usedwithout any modification to the pizza box. Because the resistancecoating draws relatively little power and operates at relatively lowtemperature, the heating element need have no insulating or mechanicalsupport and can simply be a sheet of paper with a metal coating. Theplug is disposable, easy to use, and is held securely in the socket.Multiple stacked plugs can be inserted into a single socket to servemultiple heaters or other devices. The heater is attractive andinteresting to look at and use and thus provides a natural promotionaldevice for pizza shops. Logos and other marketing slogans can be printedon the heating element, the cable, and the plug. Because all of theelements of the heater have flat substrates, economical, web-typecontinuous processing equipment may be used.

Other advantages and features will become apparent from the followingdescription of the preferred embodiment, and from the claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT

We first describe the drawings.

FIG. 1 is a perspective view of a pizza heater in a pizza box.

FIG. 2 is a perspective view of the heater element curled slightly toemphasize its flexibility.

FIG. 3 is a perspective view of the plug, paper cable, and a portion ofthe heater element of the FIG. 1 heater.

FIG. 4 is a perspective view illustrating the fabrication of heaterelements.

FIG. 5 is a perspective view of a stack of pizza boxes with heaters.

STRUCTURE

Referring to FIG. 1, to keep hot pizza pie 10 (with pepperoni 11) warmwhile it is being carried in a car, a heating element 12 of a disposableelectrical heater is placed on the bottom of the cardboard pizza box 14beneath the pizza. Electrical power is delivered to the heater from acar cigarette lighter socket via a disposable cigarette lighter plug 18connected by a disposable cable 20 to the heating element 12. Cable 20is prefolded to fit over the side wall 22 of the box and under the sidewall 24 of the box lid 16 (in FIG. 1, only a small fragment of the boxlid is shown in place as if the lid were closed).

Referring to FIG. 2, heating element 12 has a single sheet of flexiblebiodegradable kraft paper (0.006 inches thick) as a substrate 26 whichbears a sputtered nickel resistance coating 28. The sputtered coating isthin, e.g., 3000 A, to provide a resistance (between the conductivestripes 30, 32) of about 9.6 ohms for a coating area that is 8" by 8"(for a 10" pizza), or 12" by 12" for a 16" pizza. This would achieve atemperature of about 130° F. using 15 watts of power at 12 volts and1.25 amps (the required current and wattage rise proportionally with thearea of the coating). The 130° temperature is appropriate for keeping apizza warm. A pizza, when just removed from the oven, has a temperatureof about 150° F., and should thereafter be kept warm at a temperaturethat is lower than 150° F. and declines slowly over time.

Two edges of coating 28 are overcoated respectively with two metalconductive stripes 30, 32 (e.g., silver approximately 5000 A thick,having approximately ten times the conductivity of the resistancecoating). Stripes 30, 32 in turn meet (and are electrically connectedto) two other conductive stripes 34, 36 which are insulated from coating28 by a region 37. Stripes 34, 36 make connection with cable 20 at ajunction 38.

Referring to FIG. 3, cable 20 has two biodegradable kraft papersubstrates 50 and 51 in between which are sandwiched two parallel copperwires 42, 44. Paper substrate 51 is adhesive coated on the side facingsubstrate 50, but substrate 50 is not adhesive coated. At one end 46 ofcable 20, substrate 50 is skived to expose the surfaces of wires 42, 44which are then attached to two tin plated and presoldered copper tabs47, 49. The tabs are in turn connected to the heating element atjunction 38 (using conductive adhesive) so that tab 47 makes electricalcontact with heater conductive stripe 36, and tab 49 with stripe 34. Atthe other end 78 of cable 20, substrate 50 is similarly skived and cable20 is attached to plug 18 (by soldering) so that wires 42, 44respectively make electrical contact with two metal conductors 150, 152on plug 18.

Conductors 150, 152 are small strips of metal (e.g., presoldered tinplated copper) foil that are glued to plug 18. Conductor 152 folds overand lies on both faces of the plug as does conductor 154. When the plugis inserted into a cigarette lighter socket, conductor 150 touches themetal wall of the inside of the lighter socket and the leading tip ofconductor 152 touches the central contact of the socket.

Plug 18 includes a biodegradable paper substrate 54 laminated on bothsides with plastic layers 5, 57. One end 56 of plug 18 has a width wapproximately the size of (in particular slightly greater than) theinside diameter of the cigarette lighter socket. The leading end 58 ofplug 18 has tapered edges 60, 62 to make the plug easier to insert intothe socket. Along one edge of end 56, the plastic laminate extendsbeyond the paper substrate and is cut to form a row of teeth 64. Eachtooth 64 has one tapered leading edge 66 and a square trailing edge 68.As a result, end 56 is relatively easier to insert into the socket thanit is to remove. The teeth also provide a degree of adaptability to theplug, enabling it to be used in sockets having a variety ofconfigurations. In addition the gaps along the edge of the plug providedby the teeth reduce the tendency of the plug to creep out of the socketin reaction to the process of insertion. The other end 160 of the plugis square shaped, like a pizza box, for imprinting a logo of the pizzashop. Logos can also be imprinted on the heating element itself andrepeatedly along the cable.

The adhesive which holds conductor 152 on the substrate of the plug endsat point 154, and the tip of the conductor is given a bulging contoursuch that the tip extends slightly beyond the end of the plug substrateat point 156 and rises slightly above each face of the substrate. Thiscontour imparts a resiliency to the conductor which keeps the conductortip pressed against the cigarette lighter socket contact when the plugis inserted, notwithstanding any slight tendency for the plug to creepout of the socket after insertion.

Manufacture

Referring to FIG. 4, for economy, a series of heater elements are madefrom a single continuous sheet 70 of kraft paper. The sheet is coated(by sputtering or vapor deposition) with a series of resistance coatings28. Next parallel conductive stripes 30, 32 are coated (by sputtering orvapor deposition) all along the two edges of sheet 70. Conductivestripes 73 are then coated (by sputtering or vapor deposition) acrossthe sheet 70 at regular intervals. A small hole 74 is punched in eachstripe 73 thus electrically splitting the stripe 72 to form the twostripes 34, 36 (FIG. 2). Finally, sheet 70 is severed cross-wise atlocations 76 to free the individual heater elements.

Cable 20 is made by sandwiching wire from two continuous coils betweenpaper from two continuous rolls (one adhesive coated). The cable is thencut to the proper lengths, accordion folded, and skived as previouslyexplained. The combination of the wires sandwiched between the paperlayers provides a neat, compact, and attractive assembly. A paper tab 21(FIG. 2) is then glued around the folded cable to hold it compactlyuntil ready for use.

Plug 18 is made by plastic laminating a paper substrate, die cutting theteeth, and gluing the conductors onto the laminated substrate.

The heater is finally assembled by soldering one end of the cable to theplug and then soldering the other end of the cable to tabs 47, 49 whilesimultaneously gluing tabs 47, 49 to stripes 36, 34 with conductiveadhesive.

Operation

At the pizza shop, the heater is dropped into the bottom of the boxbefore the pizza is put in. In the car, the user pulls on the plug torelease tab 21, then extends the cable and inserts the plug into thelighter socket. By pressing on the plug the conductor 152 is compressedat its tip so that when the user stops pressing and the plug creeps backvery slightly, the electrical connection continues to be made, due tothe resilience of the conductor tip. The heater maintains the pizza at atemperature of, e.g., 130° F., and thus keeps the pizza both warm andcrisp.

Referring to FIG. 5, because plug 18 is flat, up to, e.g., four plugs 90may be stacked together and inserted into a single cigarette lightersocket, with each plug serving a separate heater in one of four pizzaboxes 14.

Other embodiments are within the following claims. For example, theresistance coating could be applied by other deposition processes andcould be other metals, such as tin, copper, or aluminum. The plug couldbe unlaminated cardboard. The heating element could have a differentsubstrate, such as a paper coated with a biodegradable polymer (one tenthousandth of an inch thick), with the metal coated lying on the polymer(this improves the uniformity of the electrical characteristics of theresistance coating). The resistance coating could be covered with, e.g.,a wax coating. The wires of the cable could be replaced by conductivemetal stripes, at greater cost. Foods other than pizza and non-fooditems could be heated.

We claim:
 1. An electrical plug to be inserted into an automotive typecigarette lighter socket of the kind having an inner wall of apredetermined diameter and a pair of electrical contacts, comprisingaflat assembly including a flat substrate having a width corresponding tothe predetermined diameter, and a pair of flat conductors attached tothe substrate for touching the pair of electrical contacts in thesocket.
 2. The plug of claim 1 in which the flat substrate comprisespaper.
 3. The plug of claim 1 in which the substrate further comprisesplastic laminations on both faces of the paper.
 4. The plug of claim 1in which the plug has a width slightly larger than the predetermineddiameter.
 5. The plug of claim 1 further comprising a tooth located totouch the inner wall of the socket, said tooth having a more taperedleading edge to make insertion of the plug easier and a less taperedtrailing edge to make removal of the plug more difficult.
 6. The plug ofclaim 5 further comprising a number of said teeth.
 7. The plug of claim6 wherein said teeth are formed along one edge of said substrate.
 8. Anelectrical plug to be inserted into an automotive-type cigarette lightersocket of the kind having an inner wall of a predetermined diameter anda pair of electrical contacts, comprisinga flat assembly including aflat substrate having a width corresponding to the predetermineddiameter, and a pair of flat conductors attached to the substrate fortouching the pair of electrical contacts in the socket, said plug havinga width slightly larger than the predetermined diameter, and a toothlocated to touch the inner wall of the socket, said tooth having a moretapered leading edge to make insertion of the plug easier and a lesstapered trailing edge to make removal of the plug more difficult.
 9. Amethod of using a plug that fits into a cigarette lighter socket,comprisingforming a stack including said plug and other cigarettelighter plugs, and inserting the stack into said socket.
 10. The plug ofclaim 1 or 8 further comprising a cable for connecting said plug to adevice to be powered, said cable having a flat substrate and a pair ofconductors mounted on the substrate.
 11. The plug of claim 10 whereinsaid conductors comprise wires.
 12. The plug of claim 10 wherein saidflat substrate of said cable comprises two layers with said conductorssandwiched between said layers.
 13. The plug of claim 12 wherein saidlayers are held together by adhesive.
 14. The plug of claim 13 whereinsaid layers comprise biodegradable paper.
 15. The plug of claim 10 inwhich said cable has transverse folds.
 16. The plug of claim 15 in whichthere are a periodic series of said folds along the length of thesubstrate.
 17. An electrical plug to be inserted into an automotive-typecigarette lighter socket of the kind having an inner wall of apredetermined diameter and a pair of electrical contacts, comprisingaflat substrate having two parallel edges and a third edge which connectsthe ends of said two parallel edges, and two conductors attached to saidsubstrate, one said conductor being exposed at one of the parallel edgesto touch one of said electrical contacts, the other conductor beingexposed at the third edge to touch the other of said electricalcontacts.
 18. The plug of claim 17 wherein said other conductor lies ata position midway between the two parallel edges.
 19. The electricalplug of claim 17 wherein said parallel edges are spaced apart by adistance corresponding to the diameter of the inner wall of anautomotive-type cigarette lighter socket.
 20. The electrical plug ofclaim 17 wherein said two conductors are generally flat.
 21. Theelectrical plug of claim 17 wherein said other conductor projects beyondsaid third edge.
 22. The electrical plug of claim 17 further comprisinga mechanism to impart resiliency to said other conductor.
 23. Theelectrical plug of claim 22 wherein said mechanism comprises saidconductor being contoured to rise slightly above said substrate.
 24. Theplug of claim 17 further comprising means for aiding the retention ofsaid plug in said socket.